You don't have to flush the toilet after every use.
Follow the saying "if it's yellow, let it mellow, if it's brown, flush it down!" We personally attest that this concept can prevent 50-75% of flushes.
Afraid to take such a bold risk? Follow these tips:
1) Communicate the importance to everyone in the household, so there is no confusion on why others aren't flushing.
2) Keep track of the number of flushes and no-flushes, as a reminder of how much water is being saved
3) Leave an air freshener in the bathroom, if odor is a concern.
4) Flush when company comes over, if you are concerned by what they might think (or explain it to them, maybe they'll agree it's a good idea).